Combine the 2 chocolates in the top half of a double boiler set over barely simmering water. Stir constantly until all chocolate is melted, then whisk in the corn syrup and water without removing the double boiler from the heat. Whisk until smooth and shiny. (The sauce can be made up to 24 hours in advance and refrigerated. To re-warm, stir over low heat or heat in a microwave.)
Whip the heavy cream and add the sugar when the cream starts to grow in volume. Continue whisking until light and fluffy.
Build a banana split in a tall martini glass by placing a triangle of banana leaf at the back of the glass. Cut banana in half then split them lengthwise. Dip the cut sides in coarse sugar and caramelize with a torch or place under broiler. Lay in the glass like rabbit ears. Add scoops of ice cream, then chocolate sauce, whipped cream and peanuts. Finish with a sprig of mint.